1. Field of the Invention
The present invention relates to an apparatus for controlling an internal combustion engine with a supercharging device, such as a supercharger or a turbosupercharger (simply, a turbocharger), and particularly to an electronically-controlled internal combustion engine with a supercharging device and an electronic fuel-injection system used to switch between at least a homogeneous combustion mode and a stratified combustion mode.
2. Description of the Prior Art
In recent years, there have been proposed and developed various internal combustion engines capable of operating at either one of at least two combustion modes, namely a homogeneous combustion mode where fuel-injection early in the intake stroke produces a homogeneous air-fuel mixture and a stratified combustion mode (a late injection combustion mode) where late fuel-injection delays the event until the end of the compression stroke to produce a stratified air-fuel mixture. When accelerating in an engine operating region of a lean or ultra-lean air/fuel mixture ratio leaner than a stoichiometric air/fuel mixture ratio (14.6:1), that is, during acceleration in a lean-burn mode or in a ultra-lean-burn mode), there are two ways to increase the engine power output. One way is to control or manage the air/fuel mixture ratio (A/F or AFR) toward a richer air/fuel ratio. In this case, there is a problem of increased nitrogen oxides (NOx) emissions. Another method is to increase the pressure on the air-fuel mixture by way of the supercharging device, without changing the A/F. According to the latter method, it is possible to increase the engine power output while reducing NOx emissions, when accelerating in the lean-burn mode or in the ultra-lean-burn mode. One such method has been disclosed in Japanese Patent Provisional Publication No. 7-158462.